Twenty-five or thirty years ago it became important to continuously detect the percentage of oil and water, or the percent of water and oil, in streams of well production. The well-producing facilities were being rapidly automated and one of the main lynch pins in the measurement of these systems was the arrangements for detecting percentages of oil and water in the stream. Continuous measurement of large flowing volumes of oil well production required increasingly accurate information on how much water was to be accounted for, and/or eliminated from, the well stream.
The industry recognized, from the beginning, that there was great promise in the use of a capacitance as a primary element responsive to the dielectric constant of the oil/water mixtures. Circuits with which to develop an analog voltage from a capacitance was relatively simple. There were many misunderstandings, misapplications and crude attempts to bring the capacitance into consistent contact with the mixtures.
Slowly, by fits and starts, sample systems were improved and an understanding of the dielectric constant of the mixtures accumulated. As an example, the effect of a phase reversal from water-in-oil to oil-in-water on the measurement system was appreciated. Eventually, the electric analog signal over a predetermined range of variation was produced as a dependable measurement tool. However, coordination of this instantaneous measurement with that of the flow rate of the mixture took additional time.
Direct measurement of flowing mixtures of oil and water is simple in principle. However, there was a fairly lengthy development period to gain a simple switch closure by an acceptable form of meter. Eventually, the positive displacement (P.D.) meter and turbine meter designs have been developed and accepted by the industry to the point where their simple closure of switches is regarded as a reliable structure with which to generate voltage pulses whose frequencies represent the rate of flow of the mixture passing through the meter. Finally, it has been generally recognized that with the non-linear analog signal of the capacitance probe and the flow pulses of the flow meter, there remains only the problem of coordinating these two measurements to provide continuous manifestation of the relative quantities of oil and water in the mixture.
In the past, it has appeared satisfactory to generate a voltage over a finite range with a predetermined rate of increase to compare with the capacitance analog signal. It proved a fairly simple electronic manipulation to compare this ramp voltage with the capacitance analog signal and distribute the voltage flow pulses in proportion to the division of the ramp by the capacitance analog signal. More simply stated, with a voltage ramp developed over a finite period between one and two seconds, that portion of the ramp up to the value of the capacitance analog signal would direct flow pulses to one register. That part of the ramp beyond the value of the capacitance analog signal would direct subsequent flow pulses to a second register. Therefore, the ramp would be divided by the capacitance analog signal into a water portion and an oil portion, those portions being represented by the quantity of flow pulses distributed to the registers by each portion. The drawback to this system is, that the capacitance analog signal is varying so quickly that the distribution of flow pulses is a relatively crude, or inaccurate, representation of the oil and water quantities in the mixture.
Additionally, the non-linearity of the capacitance analog signal over the predetermined range of dielectric constant variation must be compatible with the ramp over a comparable range. Obviously, the non-linearity of the capacitance analog signal and the linear variation of the ramp signal would introduce error in the flow pulse distribution. Either the ramp signal had to be given a comparable non-linear variation, or the capacitance analog signal had to be linearized.
At this point in the development of the art, it is desired to coordinate each flow pulse with the nonlinear capacitance analog signal to make a fine resolution with which to actuate the manifesting meters for the oil/water quantitative relationship in the mixture. A circuit is needed which will break each voltage pulse into a large number of fragments and distribute these components accurately between a water meter and an oil meter.